What musculoskeletal disorder in a middle‑aged adult causes inability to raise the arms above the horizontal (chest) level?

Proximal Muscle Weakness Causing Inability to Raise Arms Above Chest Level

The most likely musculoskeletal disorder causing inability to raise arms above chest level in a middle-aged adult is an inflammatory myopathy (polymyositis or dermatomyositis), which presents with symmetric proximal muscle weakness and requires urgent evaluation with CK levels, autoantibodies, and consideration of high-dose corticosteroids. 1

Critical Diagnostic Approach

Immediate Red Flags Requiring Urgent Assessment

When a patient cannot raise their arms above horizontal (chest) level, this represents Brooke score 3 upper limb weakness, which signals significant proximal muscle compromise and mandates urgent evaluation for life-threatening complications 2:

• Measure respiratory function immediately - negative inspiratory force and vital capacity - as respiratory failure can develop insidiously before sudden decompensation 1
• Assess for bulbar symptoms including dysphagia, dysarthria, and facial weakness, which indicate impending respiratory compromise 1
• Check CK and troponin urgently - elevations suggest myositis or rhabdomyolysis requiring immediate intervention 1

Pattern Recognition for Differential Diagnosis

The inability to raise arms above chest level indicates proximal muscle weakness, which narrows the differential significantly:

Inflammatory Myositis (Most Likely):

• Symmetric proximal muscle weakness developing over days to weeks is the hallmark presentation 1
• CK elevation ≥3× upper limit of normal strongly suggests inflammatory myositis 1
• Obtain myositis-specific autoantibodies (anti-TIF1γ, anti-NXP2), ANA, RF, anti-CCP 1

Myasthenia Gravis Crisis:

• Fluctuating, exercise-dependent weakness of proximal extremities or bulbar muscle groups is characteristic 1
• Obtain anti-AChR and antistriational antibodies 1
• Administer IV pyridostigmine immediately (1 mg IV = 30 mg oral) if suspected 1

Duchenne Muscular Dystrophy (DMD):

• Relevant in younger males, but the question specifies middle-aged adults
• When patients can no longer raise their hand to mouth (Brooke score 3), respiratory impairment becomes more likely 2
• Progressive weakness with proximal-to-distal progression 2

Immediate Management Algorithm

Grade 3-4 Severity (Severe Weakness Limiting Self-Care)

For suspected inflammatory myositis with inability to raise arms:

1. Hold any immune checkpoint inhibitors permanently 1
2. Initiate methylprednisolone 1-2 mg/kg IV daily or higher dose bolus for severe compromise 1
3. Urgent referral to rheumatology and/or neurology 1
4. Consider plasmapheresis for acute or severe disease - preferred over IVIG when rapid response is needed 1
5. If using IVIG, administer 2 g/kg IV over 5 days (0.4 g/kg/day), but note onset of action is slower than plasmapheresis 1

Critical Pitfall: Do not perform plasmapheresis immediately after IVIG as it will remove the immunoglobulin 1

Additional Diagnostic Workup

• Inflammatory markers (ESR and CRP) 1
• Urinalysis for myoglobinuria to assess for rhabdomyolysis 1
• ECG to evaluate myocardial involvement, as cardiac manifestations can be life-threatening 1
• EMG when diagnosis is uncertain - look for polyphasic motor unit action potentials of short duration and low amplitude with increased insertional activity 1
• MRI of affected muscle groups to identify extent of involvement and guide biopsy site 1
• Muscle biopsy when diagnosis remains uncertain after initial workup 1

Critical Medication Precautions

Avoid the following medications that can worsen neuromuscular weakness:

• β-blockers, IV magnesium 1
• Fluoroquinolones, aminoglycosides, macrolides 1
• Anticholinergic medications 1
• Hold statins immediately as they can contribute to myopathy 1

Hospitalization Criteria

Consider hospitalization for patients with:

• Severe weakness limiting mobility 1
• Respiratory involvement 1
• Dysphagia 1

Alternative Considerations (Less Likely for This Presentation)

Scapular dyskinesis causes difficulty with arm elevation but typically presents with shoulder pain and dysfunction rather than pure inability to raise arms above chest level 3, 4, 5. This is more commonly associated with shoulder disorders and acromioclavicular injuries rather than generalized proximal weakness 4.

Dropped-head syndrome from cervicoscapular muscle atrophy can occur decades after high-dose mantle-field radiotherapy, but this specifically affects neck extensor muscles resulting in inability to extend the neck, not arm elevation 2.